UV-C: Fighting Hospital Germs – without Side Effects

Center for Radiological Research equipment used to test the effect of far-UV-C light on airborne coronaviruses (Source: Columbia U.)

More than 99.9 percent of seasonal coronaviruses present in airborne droplets were killed when exposed to a particular wavelength of ultraviolet light that is safe to use around humans, a new study at Columbia University Irving Medical Center has found.

“Based on our results, continuous airborne disinfection with far-UV-C light at the current regulatory limit could greatly reduce the level of airborne virus in indoor environments occupied by people,” says the study’s lead author, radiation biophysics professor David Brenner, director of the Center for Radiological Research at Columbia University Irving Medical Center.

The sensitivity of the coronaviruses to far-UV-C light suggests that it may be feasible and safe to use overhead far-UVC lamps in occupied indoor public places to markedly reduce the risk of person-to-person transmission of coronaviruses, as well as other viruses such as influenza. In Germany alone, 400,000 to 600,000 infections with hospital germs occur every year – about 10,000 to 20,000 people die from them, according to the Robert Koch Institute, Berlin.

Within the framework of their Joint Lab GaN Optoelectronics, the Ferdinand-Braun-Institut (FBH) and Technische Universität Berlin (TUB) have developed LEDs emitting in the far ultraviolet spectral range. The LEDs emit at wavelengths around 230 nm and provide more than one milliwatt output power. Such UV-C LEDs are not yet commercially available worldwide due to technological challenges of the utilized material system aluminum-gallium nitride.

Their light does not penetrate into the living layers of the skin because of their high degree of absorption. It is therefore expected that the skin – in contrast to long-wave UV-C radiation as emitted by mercury vapor lamps, for example – will not be harmed at all or will be damaged so little that the natural repair mechanisms compensate for the effect. The researchers hope that this will help to kill MDR pathogens without any long-term side effects. Within the framework of the VIMRE project (prevention of infection with multidrug resistant pathogens via in-vivo UV-C irradiation), FBH has developed and produced an irradiation system comprising an array of 118 of these LEDs on an area of 8 cm × 8 cm. It achieves a maximum irradiation power of 0.2 mW / cm2 with more than 90 % uniformity over an area of 6 cm × 6 cm. The first prototype was delivered to the Department of Dermatology at Charité – Universitätsmedizin Berlin – for skin examinations. Another device will soon be delivered to the Institute for Hygiene and Environmental Medicine of the University Medicine Center Greifswald to clarify the microbicidal effectiveness. VIMRE is funded by the German Federal Ministry of Education and Research (BMBF) as part of the consortium “Advanced UV for Life” within the Twenty20 program.

Prototype of the UVC LED irradiation system with 118 LEDs – with it germs on the skin are supposed to be killed. The inset shows a detail of the LED array. (Source: FBH, P. Immerz)

Prototypes aimed to validate procedures

Tests carried out by the two project partners with these devices are intended to show that UV-C irradiation is suitable for killing microorganisms and especially MDR pathogens (eradication). At the same time, it is to be demonstrated that this exposure is harmless to humans as long as specific irradiation doses are maintained. This will be verified using tissue samples of human skin as well as skin and mucosa models, since the preferred habitat of microorganisms such as MDR pathogens is the anterior nasal cavity and the pharynx. For this purpose, the Charité conducts dose-dependent investigations of possible DNA damage to irradiated skin. The University Medicine Center Greifswald will determine how effectively the UV LED emitters kill MDR pathogens at 230 nm and compare the results with those of UV lamps with emission at 254 and 222 nm.

LEDs have many advantages and open up further perspectives: they are particularly small and thus permit miniaturized irradiation systems. These could be used endoscopically in body orifices or as hand-held devices. LEDs also emit only little heat and hardly put any strain on the skin. In addition, they do not require high voltage – an important safety aspect, since they are used on humans. The UV LED irradiation system is to be further developed in the future so that pathogens can be eliminated in places that are difficult to access. The device might also be interesting for corona viruses, as they can also be inactivated by short-wave UV-C light. Since SARS-CoV-2 replicates in the pharynx in the first phase, it seems plausible to use such light sources in this part of the body to prevent a Covid-19 disease.

Reference: M. Buonanno et al.: Far-UVC light (222 nm) efficiently and safely inactivates airborne human coronaviruses, Sci. Rep. 10, #10285 (2020); DOI: 10.1038/s41598-020-67211-2

Links: Light Emitting Diodes for the Ultraviolet Spectral Region, Ferdinand-Braun-Institut, Leibniz-Institut für Höchstfrequenztechnik (FBH), Berlin, GermanyDept. of Radiology, Columbia University Irving Medical Center (CUIMC), New York, NY, USA

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